HOTFIRE Project Wins Engineering Award; Homogeneous Direct Injection with Fully Variable Valve Train

Jose Michael

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The HOTFIRE head on the 3-cylinder demonstrator engine. Click to enlarge. Source: Lotus Engineering

Project HOTFIRE has taken the top award in the automotive sector in ‘The Engineer Technology + Innovation Awards 2008’ in the UK. The project team, comprising engine designers from Lotus Engineering, fuel injection specialists from Continental Powertrain and thermodynamics and mechanics experts from University College London and Loughborough University, developed a gasoline direct injection (GDI) engine concept that reduces fuel consumption by 15%. The project was funded by EPSRC (Engineering and Physical Sciences Research Council).

The end application of this project is a direct injection spark ignition engine architecture that does not require stratified lean burn combustion to achieve the approximate 15% fuel savings. This ensures that the system can be used over all speed/load ranges and eliminates the need for an expensive lean NOx trap which is usually required when lean combustion is employed.

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The Astra-based Low CO2 demonstrator. Click to enlarge.

The same architecture was adopted for the Low CO2 project, a collaboration between Lotus Engineering and Continental Powertrain with funding from the Energy Saving Trust (EST). This Low CO2 project has successfully delivered a 1.5-liter 3-cylinder mild-hybrid engine incorporating the cylinder head design used by the research and this engine has been installed in Opel Astra demonstrator vehicles. The demonstrator produces 149 g/km CO2—a reduction of 15% against the naturally aspirated 1.8-liter 4-cylinder engine version of the same vehicle—along with a 36% increase in torque and 14% more power output. (Earlier post.)

The project studied the benefits of homogeneous, early, direct injection for a spark ignition engine, using inlet valve events to minimise throttling losses. Being able to introduce the fuel separately from the air gives you freedom with how you operate the engine, there is no fuel lost to the exhaust, so hydrocarbon emissions are reduced, and you get more efficiency from the engine.

—Geraint Castleton-White, Head of Powertrain at Lotus Engineering

Two single cylinder research engines were designed and constructed by Lotus Engineering, one of which was optically accessed. The in-cylinder geometry of the two engines was identical and features a close spaced direct injection system with a centrally-mounted injector architecture.

The optical version of the engine incorporated a full length fused silica quartz cylinder liner with a full view of the pent roof of the combustion chamber and a sapphire window in the piston crown. This allowed an advanced suite of laser diagnostics to measure air motion, injection characteristics, air/fuel mixing and combustion. This engine was based at Loughborough University for detailed studies of these in-cylinder phenomena.

The second engine was placed at UCL, and was updated to the same engine architecture as the optical engine, to measure emissions and fuel economy. The principle of the investigation was to use early inlet valve closing as a means of controlling the load on the engines, with a minimum amount of throttle, and so gain significant fuel savings. The emission measurements were essential, as any fuel savings could not be at the expense of the exhaust emissions from the engine.

The engine features injectors positioned in the cylinder head and is fitted with Lotus’s electrohydraulic variable valve train system in a four-valve per cylinder configuration.

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